1. Field of the Invention
The present invention relates to an object detecting system for a vehicle, which is designed to detect an object which may possibly be an obstacle to a traveling vehicle, e.g., a moving object such as a vehicle traveling ahead of the subject vehicle, or a stationary object such as a vehicle stopped on a road, a dropped object and the like, based on transmission of an electromagnetic wave and the reception of such an electromagnetic wave.
2. Description of the Related Art
A conventionally known object detecting system, as disclosed, for example, in Japanese Patent Application Laid-open No. 8-240660, detects an obstacle existing ahead of the subject vehicle in a direction of movement of the subject vehicle based on the result of, a detection performed out by radar which transmits an electromagnetic wave, such as a laser, forwards in a direction of movement of the vehicle and which receives an electromagnetic wave reflected from the object. Thus, a warning is emitted, or an avoiding movement of the vehicle for avoiding collision of the vehicle with the object is automatically carried out.
The above known system detects only an obstacle existing on a road on which the vehicle is moving. This system is adapted to transmit the electromagnetic wave forwards in the direction of movement of the subject vehicle and in a direction substantially parallel to the road, thereby detecting only an obstacle existing ahead of the subject vehicle in the direction of movement of the subject vehicle presumably based on a steering angle, a yaw rate and the like.
However, on an actual road on which the vehicle is traveling, a footbridge and a signpost exist over the road, and/or a cateye is embedded in the surface of the road. Therefore, it is desired to avoid detecting these objects as obstacles since any of these objects are not actually obstacles. Thereupon, it is conceived that an electromagnetic wave is transmitted at a relatively narrow vertical angle to detect an obstacle only in a direction substantially parallel to the road. However, is the pitch angle of the vehicle varies due to many factors such as the acceleration or deceleration of the vehicle, the undulation of the road surface, the loaded state of the vehicle and the like. Thus, the angle of transmission of the electromagnetic wave with respect to the road varies due to the variation in pitch angle. Therefore, there is a possibility that an object, which exists on the road ahead of the vehicle in the direction of movement of the vehicle and which should be detected as an obstacle, may not be detected. In contrast, an object which exists over the road or exists on the road and which is not an obstacle, may be mis-detected.